Radio device, channel allocation method, and channel, allocation program

ABSTRACT

When there is a connection request to a base station supporting adaptive modulation from a terminal supporting adaptive modulation, the base station measures a D wave level that indicates communication environment of the transmission path. When the measured D wave level is not lower than a threshold value of D wave level at which communication is possible by a modulation method (16QAM) having larger multi-value number, the base station permits allocation of a wireless channel to the terminal. Therefore, even when the modulation method is switched from one having smaller multi-value number (π/4 shift QPSK) to one having larger multi-value number (16QAM) during communication after channel allocation to the terminal, degradation of communication quality due to the communication environment of the transmission path can be prevented.

TECHNICAL FIELD

The present invention relates to a wireless apparatus, a channelallocation method and a channel allocation program. Particularly, thepresent invention relates to a wireless apparatus that can support aplurality of modulation methods of different multi-value numbers formodulation (hereinafter referred to as multi-value number), and to amethod and a program of channel allocation when modulation method isswitched during communication in such a wireless apparatus.

BACKGROUND ART

Conventionally, in a mobile communication system such as a PHS (PersonalHandyphone System), communication is established between a mobileterminal apparatus (hereinafter referred to as a terminal or PS(Personal Station)) and a wireless base station (hereinafter referred toas a base station or a CS (Cell Station)), using a known π/4 shift QPSK(Quadrature Phase Shift Keying) modulation method.

FIG. 8A shows an arrangement of symbol points in accordance with the π/4shift QPSK modulation method on an IQ coordinate plane. Referring toFIG. 8A, more specifically, in the π/4 shift QPSK modulation method, asymbol point of a received signal corresponds to any of four signalpoints positioned concentrically on the IP coordinate plane, as is wellknown, and therefore, 2-bits of data representing any of the four signalpoints can be transmitted at one time.

Conventionally, both in the stage of establishing wireless communicationbetween the terminal and the base station through a control channel CCH(Control Channel) and in the stage of performing desired datacommunication of voice or the like through a traffic channel TCH(Traffic Channel), a fixed modulation method, such as the π/4 shift QPSKmodulation method mentioned above, is used for communication.

In recent mobile communication system, data transmission of largeramount at higher speed than the conventional voice communication isrequired, such as in the case of data communication. Therefore, methodsof modulation having larger multi-value number than the conventional π/4shift QPSK modulation method have been developed.

As an example of such modulation method of larger multi-value number,16QAM (Quadrature Amplitude Modulation) method has been known andpractically used in some type of data communications.

FIG. 8B shows an arrangement of symbol points in accordance with the16QAM modulation method on the IQ coordinate plane. Referring to FIG.8B, according to the 16QAM method, a symbol point of a received signalcorresponds to any of a total of 16 signal points on the entire plane,with the signal points being arranged in a lattice form of four pointson each quadrant, on the IQ coordinate plane. Therefore, it is possibleto transmit 4-bits of data representing any of the 16 signal points, atone time.

When a modulation method having larger multi-value number such as the16QAM method is employed as the modulation method of the PHS, symbolpoints may possibly be recognized erroneously if communicationenvironment of the transmission path is unsatisfactory (when thetransmission path has considerable noise/interfering waves). Namely,this method has a characteristic that it has higher communication rateand is more prone to reception error, than the π/4 shift QPSK modulationmethod shown in FIG. 8A.

Generally, in the stage of establishing wireless connection through CCH,routine information only is transmitted between the terminal and thebase station, and in this stage, higher rate of communication is notrequired. Therefore, communication rate attained by the conventional π/4shift QPSK modulation method is sufficient.

In data communication through TCH, however, higher rate of datacommunication has been strongly desired, in order to transmit largeamount of data.

In view of the foregoing, an idea of adaptive modulation has beenproposed, in which communication is done in the conventional π/4 shiftQPSK modulation method in the stage of establishing wireless connectionthrough CCH, and in the stage of data communication through TCH afterthe connection is established, the modulation method is switched to the16QAM method.

In the stage of establishing connection between the terminal and thebase station, by way of example, the terminal transmits a wirelessconnection request to the base station. The base station measures, as aparameter representing a state of communication environment of thetransmission path, a known RSSI (Received Signal Strength Indication)value as a D (Desired) wave level, based on a received signal powerlevel of the desired signal, determines whether the measured D wavelevel exceeds a threshold value to realize communication with stablecommunication quality under the π/4 shift QPSK modulation method, anddetermines whether a wireless channel should be allocated or not,dependent on the result of determination.

The D wave level (RSSI value) corresponds to S of the signal-to-noiseratio (S/N ratio), and therefore, when the noise N received by the basestation is known beforehand, the D wave level may be consideredequivalent to the S/N ratio.

More specifically, the threshold value is set to such a D wave levelthat satisfies a error rate BER (Bit Error Rate) that can realize stablecommunication quality when communication is done in accordance with theπ/4 shift QPSK modulation method. When the actually measured D wavelevel does not reach the threshold value, communication qualitydegrades, possibly resulting in reception error or disruption ofwireless connection, and hence normal and stable communication isimpossible.

Therefore, only when the actually measured D wave level exceeds thethreshold value, a wireless channel is allocated (that is, connection ispermitted) to the terminal requesting connection, and when the leveldoes not reach the threshold value, wireless channel is not allocated(connection is rejected).

FIG. 9 is an illustration showing, with time, a communication procedurebetween a terminal (PS) and a base station (CS), when the modulationmethod is switched as described above (adaptive modulation).

First, in the stage of establishing wireless connection, communicationtakes place in accordance with the π/4 shift QPSK modulation method. Aconnection request may be made either by the terminal or the basestation. In this example, it is assumed that the terminal transmittedthe request.

First, through a link channel establishing phase, signals related to thewireless connection request are exchanged between the terminal and thebase station. Specifically, the D wave level from the terminal ismeasured on the side of the base station, whether the measured D wavelevel exceeds the threshold value for allocating wireless channel of theπ/4 shift QPSK modulation method described above or not is determined,and if the level exceeds the threshold value, subsequent process forestablishing wireless connection is executed.

Specifically, exchange for a service channel establishing phase takesplace, and when the terminal and the base station are synchronizedthereby, message control (call control and the like) is executed betweenthe terminal and the base station. Operations thus far correspond to thestage of establishing wireless connection executed by communication inaccordance with the π/4 shift QPSK modulation method.

Thereafter, to enter the stage of data communication, assume that themodulation method is switched from the π/4 shift QPSK modulation methodto the 16QAM method, in order to attain higher communication rate.

In this case, there is a possibility that communication qualitydegrades, causing data communication failure, as represented by dottedlines in FIG. 9, because of the following reasons.

Different modulation methods have different, unique error ratecharacteristics, as will be described later, and by way of example, theπ/4 shift QPSK modulation method and the 16QAM method have muchdifferent characteristics. Therefore, even if the D wave level of asignal from the terminal at the base station satisfies the channelallocation threshold value of the π/4 shift QPSK modulation method,stable communication quality is not always ensured under the 16QAMmodulation method.

Specifically, even when normal and stable communication is possible bythe π/4 shift QPSK modulation method, wireless communication qualitydegrades when the method is switched to the 16QAM modulation method, andnormal communication possibly fails because of communication error or anaccident such as disruption of the wireless connection.

This point will be described in detail with reference to FIG. 10. FIG.10 is a graph representing relation between the communicationenvironment of the transmission path and the error rate in the receivedsignal, for the π/4 shift QPSK modulation method and the 16QAMmodulation method. It is noted that FIG. 10 is an exemplary graphallowing visual recognition of error rate with respect to the modulationmethod, and specific values are not necessarily precise.

Specifically, the abscissa of FIG. 10 represents signal-to-noise ratio(S/N ratio: considered as equivalent to D wave level) on thetransmission path, and the ordinate represents error rate BER of thereceived signal.

Similar characteristics can be seen when the abscissa is replaced by aratio of the D wave level on the transmission path to undesired signallevel, that is, U (Undesired) wave level (D/U ratio).

Generally, in the digital communication system, a signal waveformreceived on the receiving side is returned to the digital informationthat was intended by the transmission side, by a demodulating process.The digital information is binary information of “0” or “1”, andtherefore, it is basically noise-free.

However, as described with reference to FIGS. 8A and 8B, when a largenoise occurs in the middle of the transmission path, digital informationof “0” or “1” to be transmitted may be transmitted erroneously becauseof the noise.

Transmission error is caused by noise or interfering wave as mentionedabove, and from the S/N ratio (or D/U ratio) of the noise introduced tothe transmission path and the modulated wave (desired transmissionsignal wave), an error rate (BER), which indicates how frequently erroroccurs when a large amount of information is transmitted, can roughly beassessed.

Specifically, the error rate is closely related to the S/N ratio (D/Uratio) on the transmission path, and hence it can be derived bycalculation using well-known statistical theory: It is also known thatdifferent modulation method results in different error rate, even if theS/N ratio (D/U ratio) on the transmission path is the same.

Returning to the characteristic diagram of FIG. 10, the relation betweenthe S/N ratio and the error rate BER of the π/4 shift QPSK modulationmethod is plotted in dotted line, while the relation between the S/Nratio and the error rate BER of the 16QAM method is plotted inchain-dotted line.

Referring to the example of FIG. 10, assume that the error rate BER of,for example, 10⁻⁴ is to be ensured regardless of the modulation methodin order to maintain stable communication quality. From the graph ofFIG. 10, it can be seen that by the π/4 shift QPSK modulation method(dotted line), the error rate can be suppressed to 10⁻⁴ or lower withthe S/N ratio of about 6 dB or higher, whereas by the 16QAM method, theS/N ratio must be at least about 11 dB in order to suppress the errorrate to 10⁻⁴ or lower.

Such difference in error rate characteristics among various modulationmethods may lead to such a situation that, the S/N ratio of thetransmission path exceeds the threshold value of S/N ratio for stablecommunication under the π/4 shift QPSK modulation method (about 6 dB inthe example of FIGS. 8A and 8B above) in the stage of establishingwireless connection and a wireless channel is allocated in the linkchannel establishing phase, while the S/N ratio at this time is belowthe S/N ratio for stable communication under the 16QAM modulation method(in the example of FIG. 10, about 11 dB or higher): if the modulationmethod is switched in this state from the π/4 shift QPSK modulationmethod to the 16QAM method, the error rate BER degrades (in the exampleof FIG. 10 above, the error rate becomes higher than 10⁻⁴) and wirelesscommunication quality degrades, possibly causing communication error ordisruption of wireless connection.

The same applies when D/U ratio is referred to in place of the S/N ratioof the transmission path.

As described above, a conventional wireless apparatus that supportsadaptive modulation has a problem that even when wireless connection isonce established under a modulation method of smaller multi-value numberand a channel is allocated, normal communication may fail due todegraded communication quality when the modulation method is switched toone having larger multi-value number during communication.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a wirelessapparatus capable of supporting a plurality of modulation methods havingdifferent multi-value numbers and free of communication qualitydegradation even when modulation method is switched duringcommunication, as well as to a channel allocation method and program forsuch a wireless apparatus.

According to an aspect, the present invention provides a wirelessapparatus that can support two types of modulation methods havingdifferent multi-value numbers, including modulation method switchingmeans, storing means, parameter measuring means, parameter comparingmeans, and channel allocation determining means. The modulation methodswitching means switches, when another wireless apparatus to be inwireless connection with the wireless apparatus is capable of supportingtwo types of modulation methods, the modulation method between a firstmodulation method having a smaller multi-value number and a secondmodulation method having a larger multi-value number, while the wirelessapparatus is communicating with said another wireless apparatus. Thestoring means stores a first threshold value of a parameter indicativeof communication environment of transmission path, at which the wirelessapparatus can communicate with another wireless apparatus at least bythe second modulation method of the two types of modulation methods. Theparameter measuring means measures the parameter based on a signalreceived from another wireless apparatus. The parameter comparing meanscompares, when there is a connection request from another wirelessapparatus to the wireless apparatus, the stored first threshold value ofthe parameter corresponding to the second modulation method with themeasured parameter. The channel allocation determining means permitsallocation of a wireless channel to said another wireless apparatus,when it is determined by the parameter comparing means that the measuredparameter is not lower than the stored first threshold value of theparameter.

Preferably, the storing means stores in advance a second threshold valueof a parameter indicative of communication environment of transmissionpath, at which the wireless apparatus can communicate with anotherwireless apparatus by the first modulation method. When there is aconnection request from another wireless apparatus that supports thefirst modulation method but not the second modulation method to thewireless apparatus, the parameter comparing means compares the storedsecond threshold value of the parameter corresponding to the firstmodulation method with the parameter measured by the parameter measuringmeans. The channel allocation determining means permits allocation of awireless channel to said another wireless apparatus that supports thefirst modulation method but not the second modulation method, when it isdetermined by the parameter comparing means that the measured parameteris not lower than the stored second threshold value of the parameter.

Preferably, the channel allocation determining means determinespresence/absence of any empty slot and empty channel in the wirelessapparatus, and when there is no empty slot or empty channel, rejectsallocation of a wireless channel regardless of the result of comparisonby the parameter comparing means.

Preferably, the wireless apparatus further includes means for notifyinganother wireless apparatus requesting connection to the wirelessapparatus about rejection of channel allocation, when the channelallocation determining means rejects allocation of the wireless channel.

Preferably, the parameter is based on a reception signal level fromanother wireless apparatus requesting connection to the wirelessapparatus.

According to another aspect, the present invention provides a channelallocation method in a wireless apparatus that can support two types ofmodulation methods of different multi-value numbers, and the wirelessapparatus includes: modulation method switching means for switching,when another wireless apparatus to be in wireless connection with thewireless apparatus is capable of supporting two types of modulationmethods, the modulation method between a first modulation method havinga smaller multi-value number and a second modulation method having alarger multi-value number, while the wireless apparatus is communicatingwith said another wireless apparatus; storing means for storing a firstthreshold value of a parameter indicative of communication environmentof transmission path, at which the wireless apparatus can communicatewith another wireless apparatus at least by the second modulation methodof the two types of modulation methods; and parameter measuring meansfor measuring said parameter based on a signal received from anotherwireless apparatus. The channel allocation method includes the steps ofcomparing, when there is a connection request from another wirelessapparatus to the wireless apparatus, the stored first threshold value ofthe parameter corresponding to the second modulation method with themeasured parameter, and permitting, when it is determined that themeasured parameter is not lower than the stored first threshold of theparameter, allocation of a wireless channel to said another wirelessapparatus.

Preferably, the storing means stores in advance a second threshold valueof a parameter indicative of communication environment of transmissionpath, at which the wireless apparatus can communicate with anotherwireless apparatus by the first modulation method. The channelallocation method includes the steps of comparing, when there is aconnection request from another wireless apparatus that supports thefirst modulation method but not the second modulation method to thewireless apparatus, the stored second threshold value of the parametercorresponding to the first modulation method with the parameter measuredby the parameter measuring means; and permitting, when it is determinedthat the measured parameter is not lower than the stored secondthreshold value of the parameter, allocation of a wireless channel tosaid another wireless apparatus that supports the first modulationmethod but not the second modulation method.

Preferably, the channel allocation method further includes the step ofdetermining presence/absence of any empty slot and empty channel in thewireless apparatus, and when there is no empty slot or empty channel,rejecting allocation of a wireless channel regardless of the result ofcomparison in the parameter comparing step.

Preferably, the channel allocation method further includes the step ofnotifying another wireless apparatus requesting connection to thewireless apparatus about rejection of channel allocation, whenallocation of a wireless channel is rejected.

Preferably, the parameter is based on a reception signal level fromanother wireless apparatus requesting connection to the wirelessapparatus.

According to a still further aspect, the present invention provides achannel allocation program in a wireless apparatus that can support twotypes of modulation methods of different multi-value numbers, and thewireless apparatus includes: modulation method switching means forswitching, when another wireless apparatus to be in wireless connectionwith the wireless apparatus is capable of supporting two types ofmodulation methods, the modulation method between a first modulationmethod having a smaller multi-value number and a second modulationmethod having a larger multi-value number, while the wireless apparatusis communicating with said another wireless apparatus; storing means forstoring a first threshold value of a parameter indicative ofcommunication environment of transmission path, at which the wirelessapparatus can communicate with another wireless apparatus at least bythe second modulation method of the two types of modulation methods; andparameter measuring means for measuring said parameter based on a signalreceived from another wireless apparatus. The channel allocation programcauses a computer to execute the steps of comparing, when there is aconnection request from another wireless apparatus to the wirelessapparatus, the stored first threshold value of the parametercorresponding to the second modulation method with the measuredparameter, and permitting, when it is determined that the measuredparameter is not lower than the stored first threshold of the parameter,allocation of a wireless channel to said another wireless apparatus.

Preferably, the storing means stores in advance a second threshold valueof a parameter indicative of communication environment of transmissionpath, at which the wireless apparatus can communicate with anotherwireless apparatus by the first modulation method. The channelallocation program causes the computer to further execute the steps of:comparing, when there is a connection request from another wirelessapparatus that supports the first modulation method but not the secondmodulation method to the wireless apparatus, the stored second thresholdvalue of the parameter corresponding to the first modulation method withthe parameter measured by the parameter measuring means; and permitting,when it is determined that the measured parameter is not lower than thestored second threshold value of the parameter, allocation of a wirelesschannel to said another wireless apparatus that supports the firstmodulation method but not the second modulation method.

Preferably, the channel allocation program causes the computer tofurther execute the step of determining presence/absence of any emptyslot and empty channel in the wireless apparatus, and when there is noempty slot or empty channel, rejecting allocation of a wireless channelregardless of the result of comparison in the parameter comparing step.

Preferably, the channel allocation program causes the computer tofurther execute the step of notifying another wireless apparatusrequesting connection to the wireless apparatus about rejection ofchannel allocation, when allocation of a wireless channel is rejected.

Preferably, the parameter is based on a reception signal level fromanother wireless apparatus requesting connection to the wirelessapparatus.

Therefore, according to the present invention, in a wireless apparatussupporting adaptive modulation, when there is a connection request fromanother wireless apparatus similarly supporting adaptive modulation, aparameter indicative of the communication environment of a transmissionpath is measured, and allocation of a wireless channel to the saidanother wireless apparatus is permitted when the measured parameter isnot lower than a threshold value of the parameter at which communicationis possible by a modulation method having larger multi-value number.Therefore, even when modulation method is switched from one havingsmaller multi-value number to one having larger multi-value numberduring communication after connection, degradation of communicationquality can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing, with time, a communication procedurebetween a terminal and a base station in accordance with the presentinvention.

FIG. 2 is a functional block diagram representing a configuration of abase station as a wireless apparatus in accordance with an embodiment ofthe present invention.

FIG. 3 is a functional block diagram representing a configuration of aterminal as a wireless apparatus in accordance with an embodiment of thepresent invention.

FIG. 4 is a flow chart representing a method of channel allocation inaccordance with a first embodiment of the present invention.

FIG. 5 is a flow chart representing a method of channel allocation inaccordance with a second embodiment of the present invention.

FIG. 6 is a flow chart representing a method of channel allocation inaccordance with a third embodiment of the present invention.

FIG. 7 is an illustration showing, with time, a communication procedurebetween a terminal and a base station in accordance with a thirdembodiment of the present invention.

FIGS. 8A and 8B show arrangements of symbol points of π/4 shift QPSK and16QAM, on an IQ coordinate plane.

FIG. 9 is an illustration showing, with time, a communication procedurebetween a terminal and a base station in accordance with conventionaladaptive modulation.

FIG. 10 shows relation between S/N ratio on the transmission path andBER for π/4 shift QPSK and 16QAM.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention will be describedin detail with reference to the figures. In the figures, the same orcorresponding portions are denoted by the same reference characters anddescription thereof will not be repeated.

First, the principle of the present invention will be described. Thepresent invention is applicable to any wireless apparatus that supportsadaptive modulation, that is, a wireless apparatus capable ofcommunicating by a plurality of modulation methods having differentmulti-value numbers, including a base station or terminal constituting amobile communication system such as the PHS. In the embodiments of thepresent invention below, examples of the present invention applied to aPHS base station as a mobile communication system will be described.

Further, in the embodiments of the present invention below, exampleswill be described in which the π/4 shift QPSK is employed as amodulation method having smaller multi-value number and the 16QAM isemployed as a modulation method having larger multi-value number asmodulation methods of adaptive modulation. The present invention,however, is not limited to these modulation methods, and it isapplicable to any wireless apparatus that can support a plurality ofmodulation methods having different multi-value numbers.

According to the embodiments of the present invention, when there is aconnection request to a wireless apparatus supporting adaptivemodulation (hereinafter, a base station) from another wireless apparatussupporting adaptive modulation (hereinafter, a terminal), no matter whatmodulation method is used for communication at first, a threshold valueof an RSSI value, that is, D wave level (that can be consideredequivalent to the S/N ratio) as a parameter of communication environmentof the transmission path at which communication is possible under themodulation method having larger multi-value number and used commonly bythe apparatuses is compared with the D wave level measured at that timepoint, and when the measured D wave level is determined to be not lowerthan the threshold value, the base station permits allocation of awireless channel (that is, permits connection).

In short, at the initial point when the terminal connects to the basestation, whether the communication environment of the transmission pathis in a state allowing communication without degrading communicationquality when modulation method is switched to one having largermulti-value number (for example, 16QAM method) or not is determined, andif it is determined that the environment is not in a communicable state,connection itself is rejected no matter whether communication isactually done under the modulation method of larger multi-value numberor not, so as to prevent possible degradation of communication qualityexpected to occur at the time of switching the modulation method afterthe connection is established.

FIG. 1 is an illustration showing, with time, a communication procedurebetween a terminal and a base station in accordance with the presentinvention.

First, in the stage of establishing wireless connection, communicationtakes place by the π/4 shift QPSK modulation method. A connectionrequest may be made either from the base station or the terminal and, inthis example, it is assumed that the terminal transmitted the request.

First, through the channel link establishing phase, signals related tothe wireless connection request are exchanged between the terminal andthe base station. Specifically, the D wave level from the terminal ismeasured on the side of the base station, whether the measured D wavelevel exceeds the threshold value for allocating wireless channel of the16QAM modulation method having larger multi-value number as describedabove or not is determined, and if the level exceeds the thresholdvalue, subsequent process for establishing wireless connection isexecuted.

Specifically, exchange for a service channel establishing phase takesplace, and when the terminal and the base station are synchronizedthereby, message control (call control and the like) is executed betweenthe terminal and the base station. Operations thus far correspond to thestage of establishing wireless connection executed by communication inaccordance with the π/4 shift QPSK modulation method.

Thereafter, to enter the stage of data communication, assume that themodulation method is switched from the π/4 shift QPSK modulation methodto the 16QAM method, in order to attain higher communication rate.

In the conventional channel allocation method shown in FIG. 9, there isa possibility that communication quality degrades when the modulationmethod is switched to the 16QAM method, causing data communicationfailure, as represented by dotted lines in FIG. 9.

In contrast, in the embodiment shown in FIG. 1, a channel is allocated(connection is permitted) after it has been previously determined at thetime of connection that the communication environment of thetransmission path allows communication by 16QAM, and therefore, datacommunication with good communication quality is possible as representedby the solid line in FIG. 1 even when the modulation method is switchedfrom the π/4 shift QPSK method having smaller multi-value number to the16QAM method having larger multi-value number during communication.

FIG. 2 is a functional block diagram representing a configuration of abase station as a wireless apparatus in accordance with an embodiment ofthe present invention.

Referring to FIG. 2, a signal of radio frequency from another wirelessapparatus (terminal) received from an antenna 1 is subjected toreception process at an RF processing unit 2, and applied to a signalprocessing unit 3. In signal processing unit 3, a process of switchingamong a plurality of modulation methods having different multi-valuenumbers is executed, under the control by a wireless control unit 4.

The signal that has been subjected to the reception process at RFprocessing unit 2 is demodulated by the selected modulation method (π/4shift QPSK or 16QAM) at signal processing unit 3.

The demodulated received signal is applied to a main control unit 5, anddecoded to a data signal. The decoded data signal is applied to a publiccircuit, not shown, through a circuit control unit 6.

On the other hand, a data signal to be transmitted is applied to maincontrol unit 5 through circuit control unit 6 from the public circuit,not shown. The data signal encoded by main control unit 5 is modulatedby the selected modulation method (π/4 shift QPSK or 16QAM) at signalprocessing unit 3.

The modulated transmission signal is subjected to a transmission processat RF processing unit 2, and transmitted through antenna 1.

Here, operations of wireless control unit 4 and circuit control unit 6are controlled by main control unit 5.

Further, at RF processing unit 2, based on the received power level ofthe received signal, the RSSI value, that is, the D wave level ismeasured and applied to signal processing unit 3 and wireless controlunit 4.

FIG. 3 is a functional block diagram representing a configuration of aterminal as a wireless apparatus in accordance with an embodiment of thepresent invention.

A signal received by antenna 11 from the base station is applied througha switch 12 to a receiving unit 13, where reception processing takesplace. Specifically, the received signal that has been down-converted bythe oscillation frequency supplied from a synthesizer is applied to acontrol unit 16.

Control unit 16 demodulates the received signal in accordance with theselected modulation method (π/4 shift QPSK or 16QAM). The demodulatedreceived signal is converted to a voice signal and transmitted to theuser, or displayed to the user as image information at a display unit17.

Meanwhile, a transmission signal is input through an input unit 18 or atransmitter unit 20 to control unit 16, and control unit 16 modulatesthe transmission signal in accordance with the selected modulationmethod (π/4 shift QPSK or 16QAM) and applies to a transmitting unit 15.

Transmitting unit 15 performs a transmission process on the transmissionsignal. Specifically, the transmission signal up-converted by theoscillation frequency supplied from synthesizer 14 is applied throughswitch 12 to antenna 11, and transmitted from antenna 11.

The operation of synthesizer 14 is controlled by control unit 16.

The overall operation of the terminal shown in FIG. 3 is controlled byuser instructions through an I/F unit 21.

Next, FIGS. 4 to 6 are flow charts representing the methods of channelallocation in accordance with the first to third embodiments of thepresent invention. According to the first to third embodiments, themethods of channel allocation described in the following are assumed tobe executed by the base station shown in FIG. 2, in response to aconnection request from the terminal shown in FIG. 3.

The configuration of the functional block diagram of the base stationshown in FIG. 2 is actually executed by software in accordance with theflow charts of FIGS. 4 to 6, by a digital signal processor (DSP), notshown. The DSP reads a program including various steps shown in FIGS. 4to 6 from a memory, not shown, and executes the same. The program may bedownloaded from a center, not shown, through circuit control unit 6 ofFIG. 2 and a public circuit.

First, in the first embodiment shown in FIG. 4, determination as tochannel allocation is performed based on the D wave level (or S/Nratio).

Referring to FIG. 4, in step S1, the base station receives a wirelessconnection request from the terminal, through π/4 shift QPSKcommunication.

The base station constantly measures the received signal power, andbased on the result of measurement, in step S2, measures the RSSI value,that is, the D wave level, from the carrier sense level.

Then, in step S3, the measurement is compared with a threshold value ofthe D wave level that allows communication by 16QAM, which is calculatedbeforehand and stored in a memory, not shown, of the base station.

As shown in Threshold Value Table A for channel allocation in FIG. 4, inorder to attain BER necessary for 16QAM communication, the D wave levelmust be about 22 dBuV. Therefore, such a D wave level is stored as thethreshold value, in the memory (Threshold Value Table A).

In step S3, the D wave level measured in step S2 is compared with thestored D wave level, and when the measured D wave level is not lowerthan the threshold value (22 dBuV), it means that the necessary BER isensured even under 16QAM communication, and therefore, channelallocation is permitted and the control proceeds to the channelallocation procedure from step S5.

In step S3, if the measured D wave level is smaller than the thresholdvalue (22 dBuV), the necessary BER for 16QAM communication cannot beattained. Therefore, the control proceeds to step S4, in which it isdetermined that channel allocation should be rejected. In step S14, thedetermination is notified to the terminal, and in step S15, the controlenters a standby state.

If it is determined in step S3 that channel allocation is possible, theflow proceeds to step S5, in which an empty slot of the base station issearched for. If there is no empty slot found in step S6, it isdetermined in step S7 that the channel allocation should be rejectedbecause of lack of empty slot, and the flow proceeds to steps S14 andS15 described above.

If an empty slot is found in step S6, the flow proceeds to step S8, inwhich an empty channel is searched for. Further, in step S9, if there isan empty channel, the U wave level of the channel is measured andcompared with a channel allocation reference of PHS standard (STD-28),to determine whether the empty channel is in an allocatable state.

If there is no allocatable empty channel found in step S10, it isdetermined in step S11 that the channel allocation should be rejectedbecause of lack of empty channel, and the flow proceeds to steps S14 andS15 described above.

If an allocatable empty channel is found in step S10, the flow proceedsto step S12, in which information of the slot/channel to be allocated isnotified to the terminal.

Thereafter, the flow proceeds to step S13, in which a communicationchannel link is established using the slot and the wireless channel, andsynchronization burst is transmitted between the terminal and the basestation. Thereafter the modulation method is actually switched from theπ/4 shift QPSK to 16QAM, and data communication is executed through thetraffic channel TCH.

Here, it is noted that a terminal as a counterpart of communication of abase station supporting adaptive modulation does not always supportadaptive modulation similarly. By way of example, even when the basestation is capable of communication both by the π/4 shift QPSK and 16QAMmethods, the terminal requesting connection may support only the π/4shift QPSK method.

In such a case, the base station must determine whether channelallocation is possible or not to the terminal that communicates only bythe π/4 shift QPSK method. Therefore, it is necessary for the basestation supporting adaptive modulation to hold, in addition to the firstthreshold value of the D wave level for 16QAM communication, a secondthreshold value of the D wave level for π/4 shift QPSK communication,and to compare the measured D wave level with the second threshold valueto determine channel allocation, when a connection request comes from aterminal that communicates only by the π/4 shift QPSK method.

By way of example, it is desirable that the D wave level of 18 dBuVrequired for the π/4 shift QPSK is stored as the threshold value in thebase station, as shown in Threshold Value Table A for channel allocationof FIG. 4.

Therefore, in the first embodiment of the present invention, the basestation may be adapted to hold, as D wave level threshold values,threshold values that allow communication by respective ones of theplurality of modulation methods having different multi-value numbers(π/4 shift QPSK and 16QAM) as the objects of adaptive modulation.

This makes it possible to determine whether channel allocation ispossible or not for a terminal communicating by a modulation methodhaving a small multi-value number (for example, the π/4 shift QPSK)using the threshold value corresponding to the modulation method, and todetermine whether channel allocation is possible or not for a terminalcapable of communicating by a plurality of modulation methods havingdifferent multi-value numbers (for example, the π/4 shift QPSK and16QAM), using the threshold value corresponding to the modulation method(for example, 16QAM) having a larger multi-value number.

It is noted that when the reception noise level of the base station isknown (for example, 2 dBuV), as shown in Threshold Value Table B in FIG.4, not the D wave level but an equivalent S/N ratio may be used as thereference for determination. This is equivalent to the threshold valueof Table C for channel allocation of S/N ratio, shown in Threshold ValueTable C in FIG. 4. Further, in place of U wave measurement in step S9,the S/N ratio may be measured and used for determining whetherallocation is possible or not using the empty channel.

In the second embodiment shown in FIG. 5, channel allocation isdetermined based on the D/U ratio.

Referring to FIG. 5, steps S21 to S35 are the same as steps S1 to S15 ofFIG. 4, and therefore, description thereof will not be repeated. Themethod of determining allocation in accordance with the secondembodiment shown in FIG. 5 differs from the method of determiningallocation in accordance with the first embodiment shown in FIG. 4 inthat in addition to the method of the first embodiment shown in FIG. 4,channel allocation is determined based on the D/U ratio in steps S36 andS37.

Specifically, after it is determined in step S30 that there is an emptychannel, the D/U ratio is calculated from the D wave level measured instep S23 and the U wave level measured in step S29.

Thereafter, in step S36, the calculated ratio is compared with thethreshold value of D/U ratio that allows communication by 16QAM, whichis calculated beforehand and stored in a memory, not shown, of the basestation.

As shown in Threshold Value Table D for channel allocation in FIG. 5, inorder to ensure necessary BER for 16QAM communication, D/U ratio ofabout 20 dB is required. Therefore, such a D/U ratio is stored as thethreshold value in the memory (Threshold Value Table D).

In step S36, the calculated D/U ratio is compared with the storedthreshold value of D/U ratio, and if the calculated threshold value isnot lower than the threshold value (20 dB), it means that the necessaryBER is ensured even under 16 QAM communication, and therefore, channelallocation is permitted and the control proceeds to step S32.

If the calculated D/U ratio is smaller than the threshold value (20 dB),the necessary BER for 16QAM communication cannot be attained. Therefore,the control proceeds to step S34, in which it is determined that channelallocation should be rejected. In step S14, the determination isnotified to the terminal, and in step S35, the control enters a standbystate.

It is noted that, even when the base station is capable of communicationboth by the π/4 shift QPSK and 16QAM methods, the terminal requestingconnection may support only the π/4 shift QPSK method, as describedabove.

In such a case, the base station must determine whether channelallocation is possible or not to the terminal that communicates only bythe π/4 shift QPSK method. Therefore, it is necessary for the basestation supporting adaptive modulation to hold, in addition to the firstthreshold value of the D/U ratio for 16 QAM communication, a secondthreshold value of the D/U ratio for π/4 shift QPSK communication, andto compare the calculated D/U ratio with the second threshold value todetermine channel allocation, when a connection request comes from aterminal that communicates only by the π/4 shift QPSK method.

By way of example, it is desirable that the D/U ratio of 16 dB requiredfor the π/4 shift QPSK is stored as the threshold value in the basestation, as shown in Table D of channel allocation threshold values ofFIG. 5.

Therefore, in the second embodiment of the present invention, the basestation may be adapted to hold, as D/U ratio threshold values, thresholdvalues that allow communication by respective ones of the plurality ofmodulation methods having different multi-value numbers (π/4 shift QPSKand 16QAM) as the objects of adaptive modulation.

As described above, according to the second embodiment, thresholddetermination of D/U ratio is performed in addition to thresholddetermination of D wave level, and therefore, channel allocationdetermination with higher accuracy becomes possible.

Next, in the third embodiment shown in FIG. 6, channel allocation isdetermined based on the D/U ratio, as in the second embodiment.

Referring to FIG. 6, steps S41 to S51 are the same as steps S21 to S31of FIG. 5, and therefore, description thereof will not be repeated. Themethod of determining allocation in accordance with the third embodimentshown in FIG. 6 differs from the method of determining allocation inaccordance with the second embodiment shown in FIG. 5 in that in themethod of the third embodiment shown in FIG. 6, in place of the D wavelevel measured when wireless connection is requested (step S42), the Dwave level measured at the time of receiving synchronizing burst (stepS53) is used to calculate the D/U ratio.

More specifically, in step S53, the D wave level of the synchronizingburst signal received in the allocated slot is measured, and in stepS54, the D/U ratio is calculated and compared with the threshold valuein Threshold Value Table D. Comparison between the D/U ratio andThreshold Value Table D has already been described in detail withreference to the second embodiment of FIG. 5, and therefore, descriptionwill not be repeated here.

Based on the result of determination of step S54, if it is determined instep S55 that allocation should be rejected, connection to the terminalis cut in step S56, and the control enters the standby state (step S58).

On the contrary, based on the result of determination of step S54, if itis determined that allocation should be permitted, a slot is searchedfor in step S59 and the modulation method is changed in step S60.

As described above, according to the third embodiment, thresholddetermination of D/U ratio based on the D wave level when thesynchronizing burst is received is performed in addition to thresholddetermination of D wave level at the time of connection, and therefore,channel allocation determination with higher accuracy becomes possible.

In the embodiments described above, when channel allocation is rejected,only a notice thereof is sent to the terminal. The terminal and the basestation may be controlled such that when channel allocation for 16QAM isrejected, communication is established by another modulation methodhaving smaller multi-value number than 16QAM.

The terminal that has received the notification of channel allocationrejection from the base station notifies the user about the rejection bya display on a display unit (for example, display unit 17 shown in FIG.3).

FIG. 7 is an illustration showing, with time, details of a communicationprocedure between a terminal PS and a base station CS in accordance witha third embodiment of the present invention. Specifically, it shows acall sequence activated on the terminal side.

Referring to FIG. 7, on the PS side, an on-hook wireless connectionrequest is executed. Specifically, first in the control channel, a linkchannel establishing request is made from the PS to the CS.

In response, the D wave level is measured as described above, andwhether the measured D wave level is not lower than the threshold valueof D wave level for 16QAM or not is determined (first channel allocationdetermination). If it is determined that the level is not lower than thethreshold value, it is determined that channel allocation should bepermitted, the U wave is measured, and a link channel allocation istransmitted to the PS.

The exchange for the link channel allocation procedure takes place inthe control channel CCH, by the π/4 shift QPSK having small multi-valuenumber.

Thereafter, the operation proceeds to the traffic channel (TCH), whilein this stage, the modulation method is still the π/4 shift QPSK method.In this stage, first, the D wave level is again measured when thesynchronizing burst from the terminal is received. From the D wave leveland the measured U wave level described above, the D/U ratio iscalculated, and whether the calculated D/U ratio is not lower than thethreshold value of D/U ratio corresponding to 16QAM or not is determined(second channel allocation determination). If it is determined to be notlower than the threshold value, it is determined that channel allocationshould be permitted, the synchronizing burst is transmitted, well-knowncontrol signals such as SABM and UA are exchanged, and further,well-known procedures of call connection/call setting, definitioninformation, function request/response, validation are performed.

After the end of these procedures, the modulation method is switchedfrom the π/4 shift QPSK method to the 16QAM method having largermulti-value number. As described above, the D/U ratio satisfies thethreshold value corresponding to 16QAM, and therefore, even when themodulation method is switched, communication quality does not degrade.

Communication through the traffic channel thereafter takes place underthe 16QAM method. Specifically, well-known control signals such as DISCand UA are exchanged, well-known procedures such as a call, RBT andresponse are performed, and then, data communication starts.

As described above, according to the present invention, in a wirelessapparatus supporting adaptive modulation, when there is a connectionrequest from another wireless apparatus that similarly supports adaptivemodulation, a parameter indicative of a communication environment of atransmission path is measured, and when the measured parameter value isnot lower than a threshold value of the parameter at which communicationis possible by a modulation method having larger multi-value number,wireless channel allocation for the said another wireless apparatus ispermitted. Therefore, even when the modulation method is switched fromone having smaller multi-value number to one having larger multi-valuenumber during communication after connection (channel allocation) toanother wireless apparatus, degradation of communication quality due tocommunication environment of the transmission path can be avoided.

INDUSTRIAL APPLICABILITY

As the present invention prevents degradation of communication qualityat the time of switching modulation method, it is effective in awireless apparatus supporting adaptive modulation.

1. A wireless apparatus capable of supporting two types of modulationmethods having different multi-value numbers, comprising: modulationmethod switching means for switching, when another wireless apparatus tobe in wireless connection with the wireless apparatus is capable ofsupporting said two types of modulation methods, the modulation methodbetween a first modulation method having a smaller multi-value numberand a second modulation method having a larger multi-value number, whilethe wireless apparatus is communicating with said another wirelessapparatus; storing means for storing a first threshold value of aparameter indicative of communication environment of transmission path,at which the wireless apparatus can communicate with said anotherwireless apparatus at least by said second modulation method of said twotypes of modulation methods; parameter measuring means for measuringsaid parameter based on a signal received from said another wirelessapparatus; parameter comparing means for comparing, when there is aconnection request from said another wireless apparatus to the wirelessapparatus, said stored first threshold value of the parametercorresponding to said second modulation method with said measuredparameter; and channel allocation determining means for permitting, whenit is determined by said parameter comparing means that said measuredparameter is not lower than said stored first threshold value of theparameter, allocation of a wireless channel to said another wirelessapparatus.
 2. The wireless apparatus according to claim 1, wherein saidstoring means stores in advance a second threshold value of a parameterindicative of communication environment of transmission path, at whichthe wireless apparatus can communicate with another wireless apparatusby said first modulation method; and when there is a connection requestfrom another wireless apparatus that supports said first modulationmethod but not said second modulation method to the wireless apparatus,said parameter comparing means compares said stored second thresholdvalue of the parameter corresponding to said first modulation methodwith the parameter measured by said parameter measuring means, and whenit is determined by said parameter comparing means that said measuredparameter is not lower than said stored second threshold value of theparameter, said channel allocation determining means permits allocationof a wireless channel to said another wireless apparatus that supportssaid first modulation method but not said second modulation method. 3.The wireless apparatus according to claim 1, wherein said channelallocation determining means determines presence/absence of any emptyslot and empty channel in the wireless apparatus, and when there is noempty slot or empty channel, rejects allocation of a wireless channelregardless of the result of comparison by said parameter comparingmeans.
 4. The wireless apparatus according to claim 1, furthercomprising means for notifying another wireless apparatus requestingconnection to the wireless apparatus about rejection of channelallocation, when said channel allocation determining means rejectsallocation of the wireless channel.
 5. The wireless apparatus accordingto claim 1, wherein the parameter is based on a reception signal levelfrom another wireless apparatus requesting connection to the wirelessapparatus.
 6. A channel allocation method in a wireless apparatuscapable of supporting two types of modulation methods of differentmulti-value numbers, said wireless apparatus including: modulationmethod switching means for switching, when another wireless apparatus tobe in wireless connection with the wireless apparatus is capable ofsupporting said two types of modulation methods, the modulation methodbetween a first modulation method having a smaller multi-value numberand a second modulation method having a larger multi-value number, whilethe wireless apparatus is communicating with said another wirelessapparatus; storing means for storing a first threshold value of aparameter indicative of communication environment of transmission path,at which the wireless apparatus can communicate with said anotherwireless apparatus at least by the second modulation method of said twotypes of modulation methods; and parameter measuring means for measuringsaid parameter based on a signal received from said another wirelessapparatus; said channel allocation method comprising the steps of:comparing, when there is a connection request from said another wirelessapparatus to the wireless apparatus, said stored first threshold valueof the parameter corresponding to said second modulation method with themeasured parameter; and permitting, when it is determined that saidmeasured parameter is not lower than said stored first threshold of theparameter, allocation of a wireless channel to said another wirelessapparatus.
 7. The channel allocation method according to claim 6,wherein said storing means stores in advance a second threshold value ofa parameter indicative of communication environment of transmissionpath, at which the wireless apparatus can communicate with anotherwireless apparatus by the first modulation method; said method furthercomprising the steps of: comparing, when there is a connection requestfrom another wireless apparatus that supports said first modulationmethod but not said second modulation method to the wireless apparatus,said stored second threshold value of the parameter corresponding tosaid first modulation method with said parameter measured by theparameter measuring means; and permitting, when it is determined thatsaid measured parameter is not lower than said stored second thresholdvalue of the parameter, allocation of a wireless channel to said anotherwireless apparatus that supports said first modulation method but notsaid second modulation method.
 8. The channel allocation methodaccording to claim 6, further comprising the step of determiningpresence/absence of any empty slot and empty channel in the wirelessapparatus, and when there is no empty slot or empty channel, rejectingallocation of a wireless channel regardless of the result of comparisonin said parameter comparing step.
 9. The channel allocation methodaccording to claim 6, further comprising the step of notifying anotherwireless apparatus requesting connection to the wireless apparatus aboutrejection of channel allocation, when allocation of a wireless channelis rejected.
 10. The channel allocation method according to claim 6,wherein said parameter is based on a reception signal level from anotherwireless apparatus requesting connection to the wireless apparatus. 11.A channel allocation program in a wireless apparatus capable ofsupporting two types of modulation methods of different multi-valuenumbers, said wireless apparatus including: modulation method switchingmeans for switching, when another wireless apparatus to be in wirelessconnection with the wireless apparatus is capable of supporting said twotypes of modulation methods, the modulation method between a firstmodulation method having a smaller multi-value number and a secondmodulation method having a larger multi-value number, while the wirelessapparatus is communicating with said another wireless apparatus; storingmeans for storing a first threshold value of a parameter indicative ofcommunication environment of transmission path, at which the wirelessapparatus can communicate with said another wireless apparatus at leastby the second modulation method of said two types of modulation methods;and parameter measuring means for measuring said parameter based on asignal received from said another wireless apparatus; said channelallocation program causing a computer to execute the steps of:comparing, when there is a connection request from said another wirelessapparatus to the wireless apparatus, said stored first threshold valueof the parameter corresponding to said second modulation method with themeasured parameter; and permitting, when it is determined that saidmeasured parameter is not lower than said stored first threshold of theparameter, allocation of a wireless channel to said another wirelessapparatus.
 12. The channel allocation program according to claim 11,wherein said storing means stores in advance a second threshold value ofa parameter indicative of communication environment of transmissionpath, at which the wireless apparatus can communicate with anotherwireless apparatus by the first modulation method; said channelallocation program causes the computer to further execute the steps of:comparing, when there is a connection request from another wirelessapparatus that supports said first modulation method but not said secondmodulation method to the wireless apparatus, said stored secondthreshold value of the parameter corresponding to said first modulationmethod with said parameter measured by the parameter measuring means;and permitting, when it is determined that said measured parameter isnot lower than said stored second threshold value of the parameter,allocation of a wireless channel to said another wireless apparatus thatsupports said first modulation method but not said second modulationmethod.
 13. The channel allocation program according to claim 11,causing the computer to further execute the step of determiningpresence/absence of any empty slot and empty channel in the wirelessapparatus, and when there is no empty slot or empty channel, rejectingallocation of a wireless channel regardless of the result of comparisonin said parameter comparing step.
 14. The channel allocation programaccording to claim 11, causing the computer to further execute the stepof notifying another wireless apparatus requesting connection to thewireless apparatus about rejection of channel allocation, whenallocation of a wireless channel is rejected.
 15. The channel allocationprogram according to claim 1 1, wherein said parameter is based on areception signal level from another wireless apparatus requestingconnection to the wireless apparatus.